Data are the core of everything that we do in statistical analysis. Data come in many forms, and I don’t just mean .csv, .xls, .sav, etc. Data can be wide, long, documented, fragmented, messy, and about anything else that you can imagine.
Although data could arguably be more means than end in psychology, the importance of understanding the structure and format of your data cannot overstated. Failure to understand your data could end in improper techniques and flagrantly wrong inferences at worst.
In this tutorial, we are going to talk data management and basic data cleaning. Earlier tutorials will go more in depth into data cleaning and reshaping. This tutorial is meant to take what you learned in those and to help you to think about those in more nuanced ways and develop a functional workflow for conducting your own research.
A good workflow starts by keeping your files organized outside of R. A typical research project typically involves:
You can set this up outside of R, but I’m going to quickly show you how to set up inside R.
When I create an rmarkdown document for my own research projects, I always start by setting up my my workspace. This involves 3 steps:
Below, we will step through each of these separately, setting ourselves up to (hopefully) flawlessly communicate with R and our data.
Packages seems like the most basic step, but it is actually very important. ALWAYS LOAD YOUR PACKAGES IN A VERY INTENTIONAL ORDER AT THE BEGINNING OF YOUR SCRIPT. Package conflicts suck, so it needs to be shouted.
For this tutorial, we are going to quite simple. We will load the psych package for data descriptives, some options for cleaning and reverse coding, and some evaluations of our scales. The plyr package is the predecessor of the dplyr package, which is a core package of the tidyverse, which you will become quite familiar with in these tutorials. I like the plyr package because it contains a couple of functions (e.g. mapvalues()) that I find quite useful. Finally, we load the tidyverse package, which is actually a complilation of 8 packages. Some of these we will use today and some we will use in later tutorials. All are very useful and are arguably some of the most powerful tools R offers.
The second step is a codebook. Arguably, this is the first step because you should create the codebook long before you open R and load your data.
In this case, we are going to using some data from the German Socioeconomic Panel Study (GSOEP), which is an ongoing Panel Study in Germany. Note that these data are for teaching purposes only, shared under the license for the Comprehensive SOEP teaching dataset, which I, as a contracted SOEP user, can use for teaching purposes. These data represent select cases from the full data set and should not be used for the purpose of publication. The full data are available for free at https://www.diw.de/en/diw_02.c.222829.en/access_and_ordering.html.
For this tutorial, I created the codebook for you (Download (won’t work in Safari or IE)), and included what I believe are the core columns you may need. Some of these columns may not be particularly helpful for every dataset.
Here are my core columns that are based on the original data:
1. dataset: this column indexes the name of the dataset that you will be pulling the data from. This is important because we will use this info later on (see purrr tutorial) to load and clean specific data files. Even if you don’t have multiple data sets, I believe consistency is more important and suggest using this.
2. old_name: this column is the name of the variable in the data you are pulling it from. This should be exact. The goal of this column is that it will allow us to select() variables from the original data file and rename them something that is more useful to us.
3. item_text: this column is the original text that participants saw or a description of the item.
CONCATENATE() function, but it could also be done in R. The reason I do it in Excel is that it makes it easier for someone who may be reviewing my codebook.Here are additional columns that will make our lives easier or are applicable to some but not all data sets:
10. reverse: this column tells you whether items in a scale need to be reverse coded. I recommend coding this as 1 (leave alone) and -1 (reverse) for reasons that will become clear later.
11. mini: this column represents the minimum value of scales that are numeric. Leave blank otherwise.
12. maxi: this column represents the maximumv alue of scales that are numeric. Leave blank otherwise.
13. year: for longitudinal data, we have several waves of data and the name of the same item across waves is often different, so it’s important to note to which wave an item belongs. You can do this by noting the wave (e.g. 1, 2, 3), but I prefer the actual year the data were collected (e.g. 2005, 2009, etc.)
15. meta: Some datasets have a meta name, which essentially means a name that variable has across all waves to make it clear which variables are the same. They are not always useful as some data sets have meta names but no great way of extracting variables using them. But they’re still typically useful to include in your codebook regardless.
Below, I’ll load in the codebook we will use for this study, which will include all of the above columns.
# set the path
wd <- "https://github.com/emoriebeck/R-tutorials/blob/master/wustl_r_workshops/workflow"
download.file(
url = sprintf("%s/data/codebook.csv?raw=true", wd),
destfile = sprintf("%s/data/codebook.csv", data_path)
)
# load the codebook
(codebook <- sprintf("%s/data/codebook.csv", data_path) %>%
read_csv(.) %>%
mutate(old_name = str_to_lower(old_name)))First, we need to load in the data. We’re going to use three waves of data from the German Socioeconomic Panel Study, which is a longitudinal study of German households that has been conducted since 1984. We’re going to use more recent data from three waves of personality data collected between 2005 and 2013.
Note: we will be using the teaching set of the GSOEP data set. I will not be pulling from the raw files as a result of this. I will also not be mirroring the format that you would usually load the GSOEP from because that is slightly more complicated and somethng we will return to in a later tutorial on purrr (link) after we have more skills. I’ve left that code in the .Rmd for now, but it won’t make a lot of sense right now.
This code below shows how I would read in and rename a wide-format data set using the codebook I created.
# download the file
download.file(
url = sprintf("%s/data/workflow_data.csv?raw=true", wd),
destfile = sprintf("%s/data/workflow_data.csv", data_path)
)
old.names <- codebook$old_name # get old column names
new.names <- codebook$new_name # get new column names
(soep <- sprintf("%s/data/workflow_data.csv", data_path) %>% # path to data
read_csv(.) %>% # read in data
select(old.names) %>% # select the columns from our codebook
setNames(new.names)) # rename columns with our new names